The helicopter rotor probably represents one of the most difficult of all power-transmission problems in the fact that high power is required at relatively low rotational speeds. High power at low speed defines high torque, and high torque in a mechanical transmission requires large, heavy gears. In addition, since every action has an equal and opposite reaction, the shaft torques must be reacted, and this requires a tail rotor system for the shaft helicopter.

A jet-propulsion system offers certain distinct advantages in comparison with a shaft-drive system for powering a helicopter rotor. It delivers a driving torque to the rotor in the form of a tangential force at the tip of the rotor rather than by twisting a shaft at the centre of the rotor.

In reply to Dr. Jeffery's discussion, we would point out that we did not use a single property of a wave to describe the waveform and to be used as a measure of the intensity of pulsation. The parameter s was the actual cut-off ratio imposed at the source by the pulsator, whereas the ratio A/h was obtained from the differential pressure records at the meter.

The usual method of determining the static pressure distribution about a model under test often relies on guessing the required positions of the static holes before the form of the distribution is known, and subsequently adding further holes to the model where particular interest may arise. This technique can clearly prove both tedious and expensive.

Therefore interest lies in the accuracy of representation of static pressure obtained from a static tube lying on the model surface.

The prediction of the forced vibration response of rotating cantilever blading is of considerable importance in the design of turbine and compressor blading where the rotational speeds are relatively high. Non-linearities in the blades arise from the effects of Coriolis accelerations due to the rotation of the blades mounted on the periphery of the disc.

Lo and Renbarger derived the differential equations of motion of a cantilever beam mounted on a rotating disc at a given stagger angle and show, for a linear case, that the frequencies of a bar vibrating transversely to a plane inclined at an angle to the plane of rotation can be found by a simple transformation of the frequencies of vibration perpendicular to the plane of rotation. Boyce, Di Prima and Handelman applied the Rayleigh-Ritz and Southwell methods to the case of a turbine blade vibrating perpendicular to the plane of rotation and determined the upper and lower bounds of the natural frequencies.

In several recent reports reference is made to spanwise variations in the boundary layers growing in the working sections of various wind tunnels. Systematic investigations by Patel, Bradshaw and de Bray are in general agreement that these variations are caused by the screens which are fitted into the settling chambers of these tunnels to dampen out non-uniformities in the upstream flow. They conclude from their experiments that these variations will be much reduced if the downstream screen (or preferably the two downstream screens) has an open area ratio greater than about 0·57 and that these should be followed by a honeycomb to obtain the most steady and uniform flow, although a honeycomb in this position may increase the turbulence level in the working section.